Intracellular communication mediated by gap junctions is thought to underli a number of crucial cell behaviors. These include the spread of electrical and hormonal signals among populations of cells and regulation of growth an development. DNA cloning indicates that there are a number of related gap junction proteins, which we generically call connexins. 1) The functional properties of gap junctions formed from many of the identified connexins have not been described. We will use an in vitro expression system consisting of pairs of voltage clamped Xenopus oocytes to study those properties. Hybrid proteins will be functionally expressed to identify protein domains that control different behavior. 2) The identity of gap junction proteins in the lens remains unclear. There are reports suggestin that a 26 kD protein (MP26) and a 70 kD protein (MP70 are gap junction structural proteins. In addition, we have cloned CDNA for what may be another gap junction protein in lens. We will make antibodies to this new protein and determine its distribution. We will clone cDNA for MP70 to determine its relationship to MP26 and other possible gap junction proteins 3) We have identified a gap junction protein whose mRNA is present only in Xenopus early embryos. We will determine the spatial and temporal expression of the protein and attempt to modulate its expression in early Xenopus embryos. 4) We will clone cDNAs coding for gap junction proteins in Drosophila. The powerful techniques available for the manipulation of gene expression in this organism will permit close examination of possible roles of gap junctional communication in growth and development.